1. Technical Field
This application generally relates to measuring force, and more particularly to techniques used to measure force applied in connection with forming a seal.
2. Description of Related Art
Samples may be processed in a laboratory or other environment for a variety of different purposes and applications. Chromatography refers to techniques for separating sample mixtures. Common chromatographic techniques include gas chromatography (GC) and liquid chromatography (LC). With an instrument that performs LC, a liquid sample to be analyzed is introduced in small volumes for analysis. The sample may be injected into a solvent stream which is carried through a column. The compounds in the sample can then be separated by traveling at different speeds through the column resulting in the different compounds eluting from the column at different times. In connection with High Performance Liquid Chromatography (HPLC) and Ultra Performance Liquid Chromatography (UPLC), pressure is used to facilitate fluid flow in the system through the chromatographic column.
In a system that performs LC, a sample may be injected into the system using different techniques. One technique is fixed loop injection where a sample may be aspirated into a needle, positioned in a sample loop, and then carried through to the column. With fixed loop injection, the sample loop becomes part of the fluid path. Another technique is direct injection where a sample is aspirated into a needle and the sample is directly injected into the system so that the needle becomes part of the fluid path. With direct injection, after the sample is aspirated into a needle, the needle may be positioned at a surface of a sealing member. The needle has sufficient force applied thereto so that the needle tip forms a seal at the surface of the sealing member when the LC system is subsequently pressurized. The sample in the needle is then carried through to the column, such as by a solvent. In direct injection such as may be used in UPLC or HPLC systems, the sealing member is subjected to conditions that affect its useful lifetime. A component or part, such as a sealing member, having a surface used in forming a seal may be replaced, for example, when an adequate seal cannot be formed and/or maintained resulting in sample leakage. In such a case, the component or part may be characterized as having reached the end of its useful lifetime. The conditions under which the components, and surfaces thereof where seals are formed, operate may affect the lifetime, or amount of time, the component may be used in an LC or other system prior to replacement. Such conditions include the pressure applied in forming the seal between the surfaces at the needle tip and sealing member. If excessive force is applied in the foregoing, the sealing member may be subjected to additional wear further reducing its useful lifetime.